Sensitive absolute-gravity gradiometry using atom interferometry

We report the demonstration of a sensitive absolute-gravity gradiometer based on light-pulse atom-interference techniques. The gradiometer consists of two absolute accelerometers operated in a differential mode. We report a differential acceleration sensitivity of 4×10^-9g/Hz1/2 and an inferred differential acceleration accuracy of less than 10^-9g. This corresponds to a gravity-gradient sensitivity of 4E/Hz1/2 (1E=10^-9s^-2) and an accuracy of better than $1E$ for a 10-m separation between accelerometers. We demonstrate that the instrument can be used to detect nearby masses in a vibrationally noisy environment and characterize instrument sensitivity to spurious acceleration and rotation noise.